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4.5 volt led desk lamp to usb port?

Can a 4.5 volt 3 aaa batery led desk lamp be powered from a usb port? Does the .5 volts make any difference?

I think you can do it without any problem. As such led desk lamps are sturdy enough. And if you measure voltage of a new battery, many times it measures more than 1.5 volts. So in total, the voltages of three batteries many times measure around 4.8 v with brand new batteries. So these lamps are capable to withstand around 5v easily.
But if you want to be totally safe, you can add a diode in between.
sctirvn687 (author) 5 years ago
Sorry for the delay guys. Thanks for all the answers.
Stick a diode in series- that'll drop ~0.6V, use something like a 1N4001 - a beter solution than a resistor.

Steve
frollard5 years ago
not a huge difference, but if the lamp is poorly designed or built to overdrive the leds at 4.5 volts (to squeeze extra brightness out of them) or worse with no protection (resistors) then putting 5v to them could cause big problems.

Personally, I'd just hook it up to 5v. If you aren't sure adding a small resistor in series that drops half a volt (depends on the current draw).

Ideally you would take the lamp apart and find what resistor they used and what configuration for the leds, then calculate an appropriate replacement (slightly higher resistance) for the extra .5v